Prevalence and correlates of underweight among lactating mothers aged 20–49 years living in the Urban Slums of Kampala City, Uganda: A mixed-methods cross-sectional study

Suboptimal nutrient intake during lactation contributes to maternal underweight and reduced breastmilk quantity and quality, with potentially severe consequences for maternal and infant health. Although underweight prevalence among lactating mothers in urban slums is presumed higher compared to other areas, empirical data from Kampala’s slums remains limited. This study examined the prevalence and correlates of underweight among lactating mothers aged 20–49 years in Kampala’s slums. A convergent mixed methods cross-sectional study was conducted among 285 lactating mothers in Kampala’s slums. Multivariable modified Poisson regression generated adjusted prevalence ratios (aPRs), with statistical significance at p < 0.05. A prespecified multivariable modified Poisson regression model guided by the UNICEF conceptual framework and literature was fitted to identify correlates of underweight among lactating mothers. Model robustness was assessed through sensitivity analyses using three distinct covariate blocks. Ten key informant interviews with health workers explored perceptions of factors associated with higher and lower prevalence of maternal underweight. Inductive thematic content analysis was used for the qualitative data whose findings were triangulated with quantitative results for a comprehensive and better contextual understanding of findings. The average age of the lactating mothers was 29 years (standard deviation = 5). Underweight (13.7%) among lactating mothers was moderately prevalent. Correlates of underweight among lactating mothers were household food insecurity (aPR = 1.4[1.2-1.6]), household size of <5 members (aPR = 0.94[0.89-0.99]), meal frequency of ≥3 meals/day (aPR = 0.74[0.66-0.83]), and minimum dietary diversity for women (MDD‑W) (aPR = 0.91[0.84-0.96]). Results from sensitivity analyses supported robustness of the findings. Factors perceived to be associated with higher prevalence of maternal underweight included household food insecurity and working mothers. Factors perceived to be associated with lower prevalence of maternal underweight included higher meal frequency, meeting MDD‑W and fewer household members. Community sensitization on family planning, household food security, meal frequency, and dietary diversity through integrated community outreaches could improve nutritional status of lactating mothers.